The role of fault-zones on groundwater

flow in crystalline basement

Clément Roques(1), Olivier Bour (1), Luc Aquilina(1), Benoît Dewandel (2), Jean-Michel

Schroetter (3), Hélène Pauwels (4), Jean-Christophe Maréchal(2), Laurent Longuevergne(1),

Tanguy Le Borgne(1), Thierry Labasque(1), Virginie Vergnaud-Ayraud(1), Sarah Leray(1),

Rebecca Houchreutener(1), Nicolas Lavenant(1), Bruno Mougin(3), Christian Camerlynck(5)

and Stéphane Durand(6)

(1) University of Rennes 1, Rennes, France; (2) BRGM, Water Dept., New Water Resource &

Economy Unit, Montpellier, France; (3) BRGM, Regional Geological survey of French Brittany,

Rennes, France; (4) BRGM, Water Dept., Orléans, France; (5) UPMC-University of Paris 6, Paris,

France; (6) CNAM – ESGT

Groundwater flow in crystalline media

Subsurface flow

Matrix

storage (?)

Deep flow (?)

Hydrodynamic properties of fault-zones ?

Origin of water?

Sustainability resource ?

(?)

2

A multidisciplinary approach : Field site (CASPAR Project)

Structural architecture => Geology and Geophysics;

Flow => Hydrodynamic and flow logging;

Groundwater sources => Hydrogeochemistry and groundwater

dating (Anions, Cations, Traces, CFC/SF6, Noble gases).

3

The field site of Saint-Brice-en-Coglès

4

Normal faults in a graben structure

5

GW flow controlled by the main tectonic structure

6

Origin of water

7

C1C2

C3

C4C5

5 sampling campaigns at different hydrological regi mes

Hydrogeochemical compartmentalization

8

Re

go

lith

Fau

lt-z

on

e

CFC-12 vs SF6 compartmentalization

9

Regolith

Fault-zone

9

Paleo-water signature from noble gases concentratio ns

12°C

Regolith

7°C

Fault

High Water Level

Fault

Low Water Level

Recharge Temp. (°C)

0°C

5°C

10°C

10

How do we estimate mixing and origin of water?

Conservative

tracers

End-members

composition

Principal component analysis

End-members mixing analysis

DISCHARGE FRACTIONS

from each end-members

Laaksoharju et al., 2008 11

Dis

cha

rge

fra

ctio

n [

-]

Discharge

(C2)

Recharge

(C4)

Origin of water controlled by regional hydrological regime

12

Pumping dependent on storage reservoirs

139 weeks pumping test at 45 m3/h

Conclusion & Perspective

� Fault zone can present high hydraulic

properties to drive GW flow at depth;

� Various origins of waters controlled

by regional hydrological regimes;

� Yields of fault-zones are highly

dependent of storage reservoirs;

� It is NOT a unique case! => Regional

study of high yield fault-zones in the

Armoricain Massif (21 sites)

14

LOG(k) [m2]D

ep

th [

m]

15

Thank you for your

attention!